Ketazines are useful as intermediates for the synthesis of hydrazine and various methods for preparing ketazines have been developed and proposed. Recently, studies have been made extensively on the process for preparing ketazines using a ketone, ammonia and hydrogen peroxide as starting materials, and such processes are disclosed, for example, in Japanese patent publication Nos. 33083/76, 36247/76, 37638/76 and 43922/78, and Japanese patent application (OPI) No. 36615/77 (the term "OPI" as used herein refers to a "published unexamined patent application"). The processes proposed in these prior art references comprise reacting the above starting materials in the presence of a nitrile or an amide as a co-reactant as an essential component of the reaction system. However, in these conventional processes, the nitrile or the amide is converted into an amide or an ammonium salt of a carboxylic acid, respectively, as the reaction proceeds, and complicated procedures are required for separation and recovery of the amide or the ammonium salt from the reaction mixture, and also for the reproduction of the nitrile and the amide from these by-products.
Also, processes for preparing ketazines using various catalysts without nitrile or amide have been proposed. For example, Japanese patent publication No. 27642/76 proposes a process using a selenium catalyst, Japanese patent application (OPI) No. 125629/79 proposes a process using a cobalt salt catalyst, Japanese patent application (OPI) No. 135719/79 proposes a process using a palladium catalyst, and Japanese patent application (OPI) No. 135718/79 proposes a process using silica gel catalyst. However, none of these conventional processes using a catalyst has sufficient reaction rate and the selectivity to the desired ketazine and, therefore, these processes are still unsatisfactory in practicing on an industrial scale.
As a result of extensive studies on a process for preparing ketazines efficiently and in high yield, the present inventors found that such objects can be achieved by using a specific arsenic compound as a catalyst.